In recent years, the increases in the number of apparatuses connected to networks and increases in the level of performance of the apparatuses have rapidly increased the amount of traffic over the networks leading to the problem of increases in power consumption. Particularly, a network apparatus such as a switch or a router is generally kept working without being powered off, irrespective of the condition of the traffic over a network, resulting in low usage efficiency of power. The transmission rate between a network apparatus and another apparatus depends on the communication standard supported by both of the apparatuses. Thus, even when the actual transmission rate between the apparatuses is lower than a maximum transmission rate supported by the network apparatus, the network apparatus operates so as to support the maximum transmission rate, using power unnecessarily.
In the past, there has been a technology, for example, for adjusting the frequency of a clock signal to be supplied to a circuit in accordance with the amount of data actually passing through a network apparatus, for power saving (as in JP-A-2003-69607, JP-A-2007-228491, and JP-A-2002-247065, for example). There has been another technology, for example, for bundling a plurality of physical lines among switch apparatuses into one logical line and controlling the powering on or off of a port in accordance with the actual data transmission rate, whereby the line transmission rate of the logical line can be changed, and the power consumption can be reduced (as in JP-A-2007-243790). The network apparatuses in the past have had a problem that it is difficult to reduce the power consumption sufficiently or that only a special logical connection can reduce the power consumption.